A public fascination with how the elderly T-shirt company owner could have successfully poisoned to death three men, and attempted a fourth, with cyanide, kept interest at a premium.

Japan has one of the lowest crime rates in the world, so it was not ready for yet more news of mass death.

In July last year, a former disabled care home employee killed 19 and injured more than 20 in a knife attack in what is believed to be the deadliest mass killing in post-war Japan.

In early October, police arrested a man after he allegedly murdered his wife and five children and set fire to their house.

Two years ago, a man killed five people, including relatives and neighbours, in a knifing spree in western Japan.

The nine suspected victims of Japanese serial killer Takahiro Shiraishi, who dismembered them in his apartment. Picture: masamasakoro.com.

But late last month, as the black widow's murder trial continued, gruesome detail on an even more prolific serial killer hit the news.

The ‘black widow’ Chisako Kakehi poisoned four men with cyanide, killing three of them. Picture: Kyodo News/AP.

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Police outside the serial killer’s apartment in suburban Zama in Tokyo, where he killed and cut up nine people. Picture: AFP.

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Former supermarket worker and brothel scout Takahiro Shiraishi moved into an apartment and started killing.

Police were called to an apartment in Zama, a quiet suburb in southwestern Tokyo, in the search for 23-year-old Aiko Tamura, who had been reported missing. Neighbours had noticed a foul smell coming from the apartment block, but had not alerted authorities.

Inside the flat, police found severed human remains stored in picnic coolers and covered with what appeared to be cat litter. Some of the dismembered parts were cut down to the bone and secreted in tool boxes.

In all, officers uncovered two severed heads, arms, and legs among a total of 240 bone parts.

Police also found a saw, which they believed was used to cut up the bodies.

The apartment, which was located in a nondescript residential area near a train station, was dubbed the "house of horrors".

Officers arrested tenant Takahiro Shiraishi, 27, who had moved there two months previously from his parents' home, 2.5 kilometres away in the same suburb. Shiraishi's father had allegedly contacted a local real estate agent saying, "I want my son to move in right away".

Takahiro Shiraishi covers his face under arrest after police found the decaying remains of nine people in his Tokyo flat. Picture: AFP.

The 2009 high school graduate had led a previously unremarkable life, working in a supermarket for two years. A brothel in Tokyo's Kabukicho red light district had then hired him as a "scout" to lure women into the sex industry, but he was arrested, convicted and earlier this year given a suspended prison sentence.

Victim Aiko Tamura, 23.

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Serial killer Takahiro Shiraishi.

On August 22 this year, the Mainichi Daily reported, Shiraishi moved into the flat in Zama and began killing almost immediately.

He contacted potential victims via social media, targeting women who had expressed a wish to enter a suicide pact via an internet site for suicidal ideation. On his arrest, Shiraishi immediately confessed to murdering Aiko Tamura, who he said he had met through the suicide site.

But as police sifted through bank cards and other items found in Shiraishi's apartment, they began adding to the list of victims.

Eventually they would determine the remains belonged to eight women and one man.

Missing and believed to be among Shiraishi's victims were three high school girls, including a 15-year-old who had vanished in August.

Shiraishi is suspected of having lured people via Twitter, telling them he could help them with suicide plans and perhaps die with them.

On his Twitter page, Shiraishi called himself the "hanging pro" and said he wanted to help people. His Twitter profile featured a Manga image of a man with neck and wrist scars wearing a noose, with the words: "I want to help people who are really in pain. Please DM me anytime".

Serial Chisako Kakehi has been sentenced to death for poisoning to death with cyanide three men. Picture: Kyodo News/AP.

He soon discovered that what they wanted to do was talk, rather than die, but he killed them anyway.

He allegedly gave them alcohol or sleeping pills, and then strangled them until they fainted, then hanged them.

Japanese media has reported that one woman who could have become Shiraishi's next victim heard a female groaning in the background during an October telephone conversation with him. "He had given me two options. One was that he makes me unconscious by putting sleep drug in my drink and then strangles me with a rope," the woman told the Fuji network. "The other was that he strangles me with a rope from behind while I'm watching TV or something.

A Japanese Twitter page collage of the believed Shiraishi victims. Picture: @kyorotan777_go.

"If I had met with him, I may have been dismembered like other victims. I may be lucky but I'm rather scared now."

Police outside Shiraishi’s flat where he says he killed them on the day he met them. Picture: AFP.

Japanese police say Shiraishi, who has since confessed to the murders, stole thousands from some of his victims and may have also sexually assaulted some of them.

He has told detectives he killed people on the day he met them. Although he took three days to dismember his first victim, he got faster with practice.

Shiraishi is in custody awaiting his fate as police work to confirm the identity of his believed victims.

The fate of black widow Chisako Kakehi appears confirmed following her sentence to be hanged. Kakehi was convicted of murdering her 75-year-old husband Isao Kakehi, as well as common-law partners Masanori Honda, 71, and Minoru Hioki, 75, and of trying to kill her acquaintance Toshiaki Suehiro, 79.

She was first arrested in November 2014 and indicted the following month on a charge of killing Isao, who died at the couple's Kyoto home a month after their wedding.

Kakehi had been widowed in 1994 after the death of her first husband, and her fabric printing company went bankrupt. She later registered with a matchmaking service, specifically asking to meet wealthy men.

She became involved with more than ten men, enabling her to inherit an estimated $10 million, but fell into debt following her attempts to speculate in stocks and futures trading.

She poisoned four of those men with cyanide, killing three.

If you or someone you know is in need of crisis or suicide prevention support, please call Lifeline on 13 11 14 or visit www.lifeline.org.au/gethelp